For the purpose of measuring a body temperature in a short period of time, a radiation thermometer which uses an eardrum as a measurement site and measures the temperature of the eardrum in a non-contact manner has been already proposed.
An example of such radiation thermometer is described in Japanese Laid-open Patent Publication No. 117422/1986. This radiation thermometer allows a head portion of a probe unit to be inserted into an external acoustic opening so that a light-guiding tube disposed at the head portion converges heat radiation from the eardrum onto an infrared ray sensor and temperature of the eardrum is measured. A main body portion includes a black body for calibration which is controlled to be a reference temperature (36.5.degree. C.). Further, the probe unit including this infrared ray sensor is also equipped with heating control means for pre-heating to the reference temperature (36.5.degree. C.). The head portion is pre-heated to a temperature which is close to a body temperature, and with the head portion in such a condition a temperature is calibrated using the black body of the main body portion. Since this enables calibration each time measurement is executed, it is possible to ignore various causes for error. In addition, temperature of the head portion does not change even when the head portion is inserted into an external acoustic opening, and therefore, a measurement error caused by a temperature change of the head portion is overcome. That is, it is necessary to ensure that the temperature of an inner surface of the light-guiding tube is the same as the temperature of the infrared ray sensor itself, so that heat radiation from the light-guiding tube itself will not cause a measurement error. Hence, in order to avoid a temperature change in the head portion even with the head portion inserted into the external acoustic opening, the temperature of the head portion is stabilized at the reference temperature (36.5.degree. C.). In this manner, heat radiation from the inner surface of the light-guiding tube can be ignored. However, the radiation thermometer which is described in Japanese Laid-open Patent Publication No. 117422/1986 needs a heating control device of high control accuracy, and therefore, requires a complex structure and circuitry, which causes increase in size of the device and cost. Further, a long stabilizing time is necessary in order to pre-heat the head portion and control the heat portion to ensure a constant temperature. Still further, since a large amount of energy is required to drive the heating control device, this system is not applicable to a portable thermometer in which a small-size battery is used as an energy source.
Against this background, a small portable radiation thermometer with high temperature measurement accuracy which does not comprise a heating control device has been proposed.
An example of a radiation thermometer described in Japanese Laid-open Patent Publication No. 28524/1990. The radiation thermometer which is described in Japanese Laid-open Patent Publication No. 28524/1990 is the same as the radiation thermometer which is described in Japanese Laid-open Patent Publication No. 117422/1986, with respect to use of a light-guiding tube as an optical system for converging heat radiation from an eardrum. However, the radiation thermometer described in Japanese Laid-open Patent Publication No. 28524/1990 does not include a heating control device of an infrared ray sensor, but instead, temperatures of the infrared ray sensor and the light-guiding tube are approximately the same as an ambient temperature, namely, a room temperature. In addition to provision of a first temperature-sensitive sensor in the vicinity of the infrared ray sensor, a second temperature-sensitive sensor is disposed at the light-guiding tube so that a temperature is measured based on the temperatures of the infrared ray sensor and the light-guiding tube. While measurement is not allowed when a temperature difference between the infrared ray sensor and the light-guiding tube is abnormally large, when the temperature difference is smaller than a preselected set value, measurement is allowed despite such temperature difference, computation is executed considering the temperatures of the infrared ray sensor and the light-guiding tube, and body temperature data are calculated. The computation for calculating the body temperature data in the radiation thermometer is conducted by a microcomputer based on an output voltage from the infrared ray sensor, an output temperature from the first temperature-sensitive sensor which measures the temperature of the infrared ray sensor and an output temperature from the second temperature-sensitive sensor which measures the temperature of the light-guiding tube. For example, when a probe is inserted into the external acoustic opening, the temperature of the light-guiding tube gradually rises while the temperature of the infrared ray sensor stays almost unchanged. Although this creates a temperature difference between the infrared ray sensor and the light-guiding tube, as body temperature data are calculated through computation which considers these temperatures, an error due to such temperature difference is avoided despite the temperature difference.
However, the radiation thermometer described in Japanese Laid-open Patent Publication No. 28524/1990 has the following problems. That is, since body temperature data are calculated based on three variables in total, namely, temperature data of the two temperature-sensitive sensors and an output from the infrared ray sensor using a complex equation, a program for this computation installed in the microcomputer is complex and computation requires a long time. In addition, constants such as radiation rate of the light-guiding tube must be measured and set in advance for the complex equation used for the computation, and it is difficult to set the constants.
Noting this, the applicant of the present application disclosed in WO97/17887, a radiation thermometer in which based on an output voltage from an infrared ray sensor, an output temperature from a first temperature-sensitive sensor which measures temperature of the infrared ray sensor and an output temperature from a second temperature-sensitive sensor which measures temperature of a light-guiding tube, an analog circuit corrects an error which is caused by a temperature difference between the first temperature-sensitive sensor and the second temperature-sensitive sensor.
Meanwhile, U.S. Pat. No. 5,159,936 discloses a radiation thermometer which comprises a first infrared ray sensor for receiving both heat radiation from an eardrum and heat radiation from a light-guiding tube itself, and a second infrared ray sensor for receiving only heat radiation from the light-guiding tube itself, and in which an output from the second infrared ray sensor is subtracted from an output from the first infrared ray sensor and an error which is caused a temperature difference between the light-guiding tube and the infrared ray sensors is consequently corrected.
Furthermore, in the radiation thermometer described in WO97/17887, adjustment of temperature compensation of an optical system is performed on the radiation thermometer described in U.S. Pat. No. 5,159,936 so that it is possible to adjust the error with the radiation thermometer described in U.S. Pat. No. 5,159,936. However, WO97/17887 discloses only adjustment of temperature compensation of the optical system.
Further, as described earlier, the radiation thermometer which is described in Japanese Laid-open Patent Publication No. 117422/1986 requires a heating control device of high control accuracy, and therefore, requires a complex structure and circuitry, which causes increase in the size of the device and cost. In addition, a long stabilizing time is necessary in order to pre-heat the head portion and control the heat portion to ensure a constant temperature. Moreover, since a large amount of energy is required to drive the heating control device, this system cannot be applied to a portable thermometer in which a small-size battery is used as an energy source. Still further, it is further problem to perform adjustment each time a body temperature is measured.